(1) Field of the Invention:
The present invention relates to a passive seat belt system for a motor vehicle, and especially to a magnetic sensor actuation system suitable for use in a passive seat belt system of the type that a slide anchor travels along a guide rail having a bent section while dragging a webbing, said magnetic sensor actuation system featuring high reliability when a magnetic sensor for generating a warning signal or stop signal is actuated by a magnet on the slide anchor.
(2) Description of the Related Art:
To date, certain passive seat belt systems have been described where a webbing is automatically applied to an occupant at the same time as the person sits in a car seat and is hence restrained and protected safely by the webbing in the event of a vehicular accident. The construction of a guide rail portion of a passive seat belt system is shown in FIG. 1.
In the illustrated passive seat belt system, a slide anchor 14 to which one end of an occupant-restraining webbing 16 [or a buckle 13 latched with a tongue 15 at one end of the webbing 16 and releasable in the event of an emergency (which may hereinafter be called "ERB"), a tongue 15 latched in the ERB 13 attached to the webbing 16, or the like] is attached is caused to travel on a guide rail 5 in the direction of the length of the vehicle along a roofside 2. The slide anchor 14 is movable between both ends of the guide rail 5. By the movement of the slide anchor 14, the webbing 16 is carried away from or toward an associated occupant seat so that a space is formed to allow the occupant to enter or egress from the vehicle and the webbing 16 is automatically applied to the occupant after he sits in the occupant seat.
A magnet disposed in a magnet casing on the slide anchor 14 actuates magnetic sensors 6-12 attached near the guide rail 5 at desired positions between both the ends of the guide rail 5, thereby generating signals each of which is used as an anchor stop signal, a passing signal or a warning signal.
FIG. 21(a) shows a first example of a conventional magnetic sensor actuation system. FIG. 21(b) is a cross-sectional view taken in the direction of arrows XXI(b)--XXI(b) of FIG. 21(a).
The ERB 13 is attached to the slide anchor 14 which travels on and along the guide rail 5. A tongue 15 to which a webbing 16 is fastened at one end thereof can be latched in the ERB 13. The ERB 13 is also formed as a magnet casing 26, so that a magnet 18 is received therein while being supported by a spring 19. When the tongue 15 is inserted into and latched with the ERB 13, the spring 19 is compressed to bring the magnet 18 closer to the guide rail 5, whereby the magnetic sensor 6 is actuated.
The slide anchor 14 must be able to travel past a sharpest bent section of the guide rail 5 when the slide anchor 15 moves on and along the guide rail 5. It is thus necessary to design the configuration of the magnet casing 26 in such a way that the casing 26 does not interfere with the guide rail 5 or a trim 20 even at the most sharply bent section. In the case of this example, both corners are cut away to minimum necessary extent as indicated at b. Inside the magnet casing 26, the magnet 18 is positioned as closely as possible to the trim 20 as indicated by a clearance c.
Nevertheless, the magnet 18 is located unduly remotely from the guide rail 5 at a position where the magnetic sensor 6 is supposed to be actuated. Although this position is at a straight section of the guide rail 5 in the drawing, the same problem also arises where the section has only a gentle bend. Obviously, the distance between the magnetic sensor 6 attached near the guide rail 5 and the magnet 18 becomes substantially greater as indicated by d.
One example of such magnetic sensor actuation systems is disclosed in Offenlegungsschrift (W. German Patent Publication No.) 37 43 550A1.
A second example of a conventional magnetic sensor actuation system is illustrated in FIG. 22(a). FIG. 22(b) is a cross-sectional view taken in the direction of arrows XXII(b)--XXII(b) of FIG. 22(a).
This second example is identical to the first (FIG. 21) except for the configuration of a magnet casing 26. The magnet casing 26 is rectangular. Without cutting away both corners, the magnet casing 26 is arranged away in toto from the guide rail 5 so that corners b come most closely to the trim 20 at the most sharply bent section of the guide rail 5.
Despite the design permitting the magnet 18 to come closest to the trim 20 when at the sharpest section of the guide rail 5, where the distance between the magnet 18 and the trim 20 is reduced approximately to c, the distance becomes greatest at the straight section as indicated by d.
In a magnetic sensor actuation system of the type where a magnetic sensor provided near a guide rail is actuated by a magnet on a slide anchor, a magnet casing tends to interfere with the guide rail or trim at the most sharply bent section of the guide rail as described above. To overcome this problem, it is necessary to cut away portions of the magnet casing where such portions may interfere with the guide rail or trim.
The determination of the configuration of the magnet casing on the basis of the most sharply bent section may however result in a large distance between the magnet and the magnet sensor depending on the position of arrangement of the magnet when one wants to arrange the magnetic sensor at a straight section or at a gently bent section for actuation at that point. As a result, it becomes difficult to control the magnetic force which reaches the magnetic sensor, so the magnetic sensor may be accidentally actuated, for example, by a shock or under the influence of an external magnetic body.
To cope with the above problem, use of a larger magnet, an increase of the magnetic force and/or enhancement of the sensitivity of each magnetic sensor could be considered. Both size and cost reductions are however desired for such magnets and magnetic sensors, and there are also physical limitations to the degree of such modifications. In practice it is therefore difficult to adopt this method.